Data recording, also referred to herein as data acquisition and/or data logging, can be used to record and store information gathered from sensors, generally over a time period of interest. Due to limitations that can exist with regards to the amount of information that can be stored by data recording systems, or the desire to minimize the amount of data to be subsequently analyzed, it can be desirable to trigger, i.e. initiate a data recording event only upon the occurrence of a specific condition or event that signals the beginning of the time period of interest.
For example, one or more trigger signals (e.g. output signals from one or more sensors) can be monitored and a data recording event initiated only when the level of a monitored trigger signal meets a given criteria, for example, whereat the signal level falls below or rises above a trigger threshold value. In this manner the memory within a data recording apparatus can be more efficiently allotted to the time period of interest, and recording of and subsequent analysis of sensor data that may not be of particular interest can be avoided.
False triggering of a data recording event can occur if the quiescent, i.e. background level of the monitored sensor signal drifts over time, and the amount of quiescent signal drift is sufficient to cause the apparent signal level to exceed a triggering criteria. Quiescent level signal drift is defined herein to be a change in the signal level output from a sensor due to an influence or environmental parameter other than the parameter the sensor is intended to measure. In one non-limiting example, it has been found that temperature deviations can cause quiescent level signal drift in some acceleration sensors. The present invention provides methods to automatically adjust trigger threshold values (i.e. triggering criteria) to compensate for drift in the quiescent level of the trigger signal, thereby avoiding false triggering of data recording events which could cause a data recording system to record data during periods other than the period of interest.